The cordless powered surgical tool has become an important instrument for performing a number of different surgical procedures. Generally, this tool includes a handpiece in which an electrically driven motor is housed. Power to energize the motor is supplied by a battery that is usually removably attached to the handpiece. A gear assembly and a coupling assembly transfer the rotary power developed by the motor to a cutting accessory. Typically, the coupling assembly is designed to removably hold the cutting accessory to the rest of the tool. Generally these tools, like other tools are used for separating and or removing hard and/or soft tissue from a patient.
A cordless powered surgical tool, as the name implies, does not have a cord to serve as a power conduit from an external source. This eliminates the need for surgical personnel to concern themselves with sterilizing a cord so that it can enter a sterile surgical field during a surgical procedure and/or ensuring that during a surgical procedure an unsterilized cord is not inadvertently brought into the surgical field. Another benefit a cordless surgical tool offers is that the elimination of the cord result in the like elimination of the physical clutter and field-of-view blockage the cord otherwise brings to a surgical procedure.
The Applicant's U.S. Pat. No. 5,747,953, CORDLESS, BATTERY OPERATED SURGICAL TOOL, issued May 5, 1998, and incorporated herein by reference, discloses a trigger assembly and control circuit suitable for integration into a cordless surgical tool. The particular tool described in this document is a drill. This type of tool has a linkage and a coupling assembly that are positioned to cause a drill bit to be driven in a rotary motion. The trigger assembly disclosed in this patent has two triggers. Collectively, the trigger assembly and control circuit are configured so that depression of one trigger will cause the motor shaft to rotate in a first direction, arbitrarily, forward rotation. Depression of the second trigger will cause the motor shaft to rotate in a second direction, arbitrarily, reverse rotation. The trigger assembly and control circuit are further configured so that simultaneous depression of both triggers will result in current being supplied to the motor in such a pattern that it oscillates in forward-reverse-forward-reverse movement.
The assembly disclosed in U.S. Pat. No. 5,747,953 has proven quite useful in many powered surgical tools. It has proven especially useful for integration in powered surgical tools that have tissue working cutting accessories that are designed to rotate around their longitudinal axes. Accessories that are so driven include drill bits and wires which are driven by drills and/or wire drivers.
However, there are limitations associated with other cordless surgical tools, specifically, saws. Generally, a powered surgical saw is a powered surgical tool with a linkage that causes the associated coupling assembly to move in a repetitive back-and-forth pattern. The coupling assembly holds a blade that is designed to cut tissue. Some saws have a linkage assemblies designed to move the complementary saw blades back and forth in a reciprocating pattern, along the longitudinal axes of the associated blades. Other saws have linkage assemblies that move the associated blades in a sagittal or oscillating movement, specifically so that the blades pivot back and forth.
One of these limitations is associated with the fact that, by the very nature of its method of use, a saw blade engages in repetitive back and forth action. As a result of this motion, the blade is invariably repetitively forced against components of the coupling assembly that holds the blade to the saw. Components forming the linkage assembly and coupling assembly similarly repetitively contact each other as a result of the bi-directional movement in which these components engage. This component contact results in an appreciable amount of noise being generated when a saw is actuated. This noise, at a minimum, can make it difficult to hear other sounds in an operating room. This noise can further be distracting to the surgeon and serve as one of the environmental factors that contribute to the stress surgical personnel experience when performing a procedure.
One means by which surgical personnel have tried to reduce the noise developed by a saw or other powered surgical tool is to run the tool at less than its highest speed. Typically this is the free speed, the no load speed, of the motor integral with the tool. Typically, this speed control is performed by manually depressing the trigger integral with the tool so that it is only partially depressed. Often a surgeon will operate the tool in this manner in the short time period before the associated cutting accessory is pressed against the tissue the accessory is intended to work. Then, as the motor speed drops as a consequence of the motor developing torque, the surgeon will adjust the pressure placed on the trigger to maintain the operation of the motor at the desired speed. While this method has proven somewhat successful in reducing tool-generated noise, it requires the surgeon to concentrate on the extent he/she has depressed the trigger integral with the tool. Thus, the surgeon has to devote some attention to the trigger setting; this may distract from the surgeon's ability to concentrate on other aspects of performing the surgical procedure.
Another method some surgeons find useful in reducing tool noise is to perform the surgical procedure with a slower speed tool. This type of tool, in comparison to its higher speed counterpart, generates less noise. It should also be apparent that, in comparison to a high speed tool, the lower speed tool is less powerful and may not be able to cut tissue as fast. In some instances, the lower speed tool may not even have the power to perform the task that can be accomplished with the higher speed tool. Consequently, in a facility where surgeons find a lower speed tool useful, the facility typically also finds it desirable, if not necessary, to also have the higher speed tool available. This latter tool is thus present for use by surgeons that prefer its faster operation and do not object to the noise. It is also necessary to have the higher speed tool ready for situations where it can perform tasks that are difficult, if not impossible, to accomplish with the lower speed unit. This essentially requires the hospital or other surgical facility to, in a sense, double the number of tools it has available in order to accommodate for the preferences of individual surgeons. This near duplication adds to the expense associated with providing a surgical facility.